Of course anon, we all know that. However methods in which a mangaka writes a TEEN ROMANCE (yes that's what CSM Part 2 is primarily) is not by making characters jump into a fight immediately but rather by making them bond first through silly interactions, funny dialogues, unexpected actions like running around the city going to a brothel and such and only then later to they start fighting. And finally the most important ingredient, dramatic emotionally charged sexual interactions. You're forgetting Yoru and Katana are only there with Denji to FIGHT him, but instead of jumping into a fight immediately they're running around the city doing stupid shit because this is primarily a teen romance and coming-of-age story. Same will happen in the sushi place because Fumiko will be off duty. She has a special bond with Denji, both intimate and sexual in nature but primarily she wants to save him too like Asa. The difference between Fumiko and Asa is that Fumiko isn't as naive nor misguided as Asa, so she is no one else's pawn. With her Denji stands a chance of survival. She can offer him a chance to run away from both PS and Kiga/Church/War devil. Whether she's successful of not is waiting to be unraveled. As for Yoshida, he will do a 180 with Asa and instead of arresting her he'll offer to help her because at that point she will be completely emotionally scarred by Denji.